The overall goal of this project is to identify major molecular alterations in carcinoma of the breast since, in marked contrast to a number of other cancers, the molecular events leading to breast cancer remain unknown in all but a small minority of cases. The hypothesis to be tested is that breast cancer harbors multiple molecular alterations that result in altered pattern of gene expression and altered cellular phenotypes. The primary avenue to identify relevant molecular alterations is to detect consistent changes in the expression of genes. Based on our experience with customized cDNA arrays of breast specific genes, we believe that new, high-throughput technologies offer an unprecedented to study the molecular biology of breast cancer. In this project, we will conduct a more intensive analysis of a larger panel of breast tumors, using customized microarrays carrying approximately 2000 genes/ESTs. This will allow us to derive a comparative gene expression profile between normal breast epithelial cells, atypical ductal hyperplasia, DCIS, and invasive cancer. From this profile, we will identify clusters of co-expressing genes associated with specific stages of the disease, and determine the frequency and relative timing of change of expression of newly identified markers at different stages of progression. Finally, we will attempt to define the clinical relevance of the identified mutations or changes in gene expression to prognosis, disease aggressiveness, age of onset, race and other biologic determinants. This will lead to the recognition of many more genes that play a crucial role in breast carcinogenesis. Identifying these alterations will provide markers for diagnosis and management of breast cancer patients, identify potential targets for molecular therapeutic interventions, and, through mechanistic studies in collaboration with other projects, lead to a better understanding of the biochemistry and pathogenesis of this cancer.